The method the Catholic Church uses to select their leader has remained virtually unchanged for the last 800 years. But how does the Papal Conclave actually work?

The system is remarkably democratic with a strong emphasis on working through multiple rounds of voting until a clear consensus emerges. Under the current rules, only Cardinals under the age of 80 are allowed to cast a vote. Officially candidates for Pope need only be male and Catholic although in reality Pontiffs have only ever been chosen from the ranks of Cardinals for centuries.

There’s no age limit on who can become Pope but given that Benedict was already in his late seventies when he took up his position and lasted a little less than eight years before his surprise retirement there is an expectation that Conclave will opt for someone in their late 50s or early 60s this time around.

This afternoon, after a special morning mass, the 115 Cardinals of voting age will gather inside the exquisitely decorated Sistine Chapel – home of all the Papal Conclaves since 1858. At 4.45pm local time the shout “extra omnes” (everybody out) will ring out and the Cardinals – who are sworn to an oath of secrecy – will be locked inside the Conclave until they can choose a successor.

We may get the first voting round today but there’s no guarantee. Through a mixture of speeches, prayer, reflection – and let’s not forget intense political jostling – Cardinals whittle down candidates through successive rounds of voting.

The Cardinals themselves sit on both sides of the Sistine Chapel. The names of nine Cardinals are chosen at random to officiate and organise the vote. Three become Scrutineers, whose job it is to oversee the vote. Three more collect the votes and three more revise them.

A Pope is only elected when a single candidate receives a two-thirds majority. Sometimes Pope’s are chosen quickly when a strong candidate emerges. However from the 34th ballot onwards, the Conclave only votes between the two front runners who gained the most votes in the previous round. Incidentally the longest Papal Conclave, in the late thirteenth century, lasted the best part of three years thanks to massive political infighting. Three voting Cardinals died during the process.

The ballot itself is secret and was introduced on 1621 by Gregory XV to try and avoid overt politicking but the Conclave is inevitably a hotbed of competing factions who wish to see their man come out on top. During each ballot Cardinals write the name of their choice, ideally in distorted handwriting to disguise their identity.

The ballot papers are then burned in a small fire inside the Sistine Chapel. The black smoke which is produced by the fire tells the crowds waiting outside that a new Pope has yet to be chosen.

When one candidate has finally won two-thirds of the vote a new Pope is elected. The Cardinal Dean then calls the candidate to the front of the chapel and asks whether they are willing to accept. If the answer is yes, the new Pope is then asked to choose his new Papal name. Although the Pope is seen as the successor of St Peter, none have chosen Peter for their Papal name, partly to avoid comparisons to the founder the Roman Catholic Church and partly because of an ancient prophecy that a new Pope called Peter will precede the end of the world.

With a Pope now duly elected the ballot papers are burned once more with an additive placed in the fire that turns the smoke white informing the world that a new Pontiff has been chosen.

In the weeks leading up to the Conclave Vatican tailors get to work on creating three Papal robes in small, medium and large. The new Pope is led into the Room of Tears adjacent to the Sistine Chapel where he dons his new white robes and red slippers. The Pope is then presented to the crowds who have gathered in the Vatican from the main balcony of St Peter’s Basilica with the famous words: “Annuntio vobis gaudium magnum: Habemus Papam!” (I announce to you with great joy we have a Pope.)

APPROXIMATE SCHEDULE FOR THE CONCLAVE

The voting process follows a set ritual every day until the Catholic Church has a new leader. Here is an approximate schedule. Local time listed first.

— 4:45 p.m.-8 p.m. (11:45 a.m.-3 p.m. EDT; 1545-1900 GMT): Each cardinal takes an oath, most likely followed by the first vote. If the vote yields a new pope, white smoke will emerge from the chimney; if not the smoke will be black.

After three full days of voting, the cardinals break for a day of prayer and reflection, then resume for another seven ballots. The first pause will be on Saturday if no pope has been selected before that.

THE SMOKE

Smoke will emerge from the chimney once at the end of the morning session — about 12 p.m. (7 a.m. EDT; 1100 GMT) — and again at the end of the afternoon session — about 7 p.m. (2 p.m. EDT; 1800 GMT). But if an earlier vote yields a pope, white smoke would emerge at that time, ending the conclave.

Once white smoke emerges from the chimney, a bell at the St. Peter's Basilica rings. Within an hour, the man who was selected emerges onto the balcony and his identity is known.